I think many people just don't realize that Udemy is a "marketplace"[1]. Yes, anyone can publish a course there, provided it meets some requirements. In the early days, Udemy's stated goal was to "democratize online education"[2].

There is an "Instructor Identity Verification Process"[3] which should make sure publishers own the content. No idea why it didn't prevent this case.

There is no "review by experts in the field". Whoever publishes a course is responsible for its content. If a course is inaccurate users will give it bad reviews and it won't sell. And in any case buyers get a 30-day money back guarantee.

There is an online form to report copyright violations[4], which looks simple enough to me.

[1] https://about.udemy.com/ [2] https://readwrite.com/2010/05/11/online-learning-startup-ude... [3] https://support.udemy.com/hc/en-us/articles/229234067-Instru... [4] https://copyright.udemy.com/hc/en-us